This application is responsive to the NCI specific opportunity: Exploratory Research in the Development of Vaccines for AIDS-associated Malignancies using the RC-2 "Grand Opportunities" mechanism, RFA-0D- 09-004. Merkel Cell Carcinoma (MCC) is an uncommon, aggressive neuroendocrine skin cancer that afflicts approximately 1,500 Americans each year. MCC is more than twice as likely to be lethal when compared to malignant melanoma. Furthermore, MCC has an increasing health impact as its reported incidence has more than tripled in the past 20 years. MCC incidence is strongly associated with T cell immune dysfunction in epidemiologic studies. Indeed, MCC incidence is 10- to 30-fold increased in people with clinically recognized T cell dysfunction including HIV, solid organ transplant recipients, and chronic lymphocytic leukemia patients. Importantly, in immune suppressed patients, MCC sometimes regresses when immune function is restored suggesting immune- based therapies may be effective in this cancer. Recently, a new human polyomavirus (Merkel cell polyomavirus, MCPyV) was discovered and appears to be involved in the pathogenesis of approximately 80% of MCCs. Importantly viral proteins are expressed in advanced and metastatic MCC tumors. Our preliminary data demonstrate that these viral proteins are typically capable of stimulating both humoral and cellular immune responses in MCC patients and controls. Furthermore, we have identified several mechanisms that MCC tumors use to escape from these immune responses. Characterizing MCPyV biology and immunology offers hope of substantial progress in understanding the pathogenesis, prognostic markers, and treatment of MCC. We propose to take advantage of the special opportunity provided by the NCI's support for "Development of vaccines for AIDS-associated malignancies" to catalyze significant progress in this field. Specifically, we will investigate the potential of rational immune- based therapy for this disease by capitalizing on three of our key assets: a uniquely complete and expanding set of MCC clinical and tissue resources, established expert immunology collaborators, and our recent insights into how this cancer evades the immune system. Despite the importance of T cell function in controlling this cancer, the immune evasion strategies employed by MCC remain poorly characterized. Our preliminary data show that these tumors often down- regulate MHC class I, typically have a sparse infiltrate of T cells, and abundantly express microRNAs associated with natural killer (NK) cell inhibition. Moreover, evidence of T- and NK-cell invasion into MCC tumors was strikingly clinically and statistically associated with improved survival in a test set of 22 cases and in an independent validation set of 35 MCC patients. We will test the hypotheses that immune evasion mechanisms newly identified in MCC are associated with survival and that Merkel polyomavirus-targeted immune therapy is promising in the rational treatment of this HIV-associated malignancy. We propose three Aims to characterize the immune evasion strategies adopted by MCC and begin the process of developing rational vaccine or adoptive immunotherapy for this disease. Aim 1: Define the mechanisms and prognostic significance of T and NK cell evasion in two large independent MCC cohorts. Aim 2: Define the cellular immune response against the Merkel polyomavirus in normal individuals and MCC patients. Aim 3: Generate MCPyV-specific T cells and measure killing of APC expressing Merkel polyomavirus proteins. These aims are feasible during the proposed period because of our extensive preliminary data, established MCC resources and our expert immunologic collaborators. An improved understanding of the relevant immune evasion mechanisms and developing the means to overcome them would have a rapid impact on prognosis and therapy of MCC as well as potentially offer insight on prognosis and treatment strategies for other cancers. PUBLIC HEALTH RELEVANCE: Merkel Cell Carcinoma (MCC) is an HIV-associated skin cancer that is twice as lethal as melanoma and strongly associated with a new human polyomavirus, MCPyV. Working with expert immunology collaborators, we will use our repository of clinically annotated blood and tissues from several hundred patients to expand on our preliminary data suggesting extensive evidence of immune evasion mechanisms in use by MCC. Specifically, we will define the nature of the cellular immune response to MCPyV as a key initial step toward developing rational, immune-based strategies to treat this cancer.